Preparation of fixing powders



United States Patent PREPARATION or FIXING POWDERS Donald J. Kridel, Edwin S. Wiitala, and Joseph Gail Stampfli, Rochester, N. Y., assignors to Eastman Kodak gompany, Rochester, N. Y., a corporation of New ersey No Drawing. Application July 26, 1954, Serial No. 445,942

1 Claim. (Cl. 95-88) This invention relates to the preparation of photographic fixing powders and more particularly to an improved method of preventing dust formation during mixing of the component powders making up the fixing formula.

Photographic acid fixing powders may be prepared by introducing the several powder components of the mixture in proper proportions into a rotating blender-drier in which the several components are tumbled to produce thorough mixing and drying.

Heretofore, very fine sprays of Water have been introduced into the rotary blender above the tumbling fixing powders. These fine sprays produce an agglomeration of the fine dust particles and cause them to be restored to the main bulk of the tumbling powder. The small moisture content thus taken up by the tumbling powder was dried out or controlled within desired limits by the heat applied to the drier.

While the water spray is effective, a more effective dust bonding spray is desirable. In fact the requirements of a satisfactory bonding agent are:

1. Its use must enhance the degree of dust elimination over that provided by spraying with pure water.

2. It must give a granule less liable to revert to dust upon tumbling or mixing.

3. It must be water soluble, impart negligible color to the product, not salt out upon solution of the other components, cause no appreciable tendency of the solution to give a persistent foam and not make the product or solution therefrom more prone to bacterial or fungus growth.

4. It must not impair the keeping properties of the product in regard to tendency to sulfurize or cake.

An object therefore of the present invention is to provide improved bonding agents for laying dust during mixing of the powder like components of photographic fixing powders. Other objects will appear hereinafter.

In accordance with the present invention we have found that solutions of the following materials are excellent bonding agents for reducing dustiness of photographic fixing powders when they are prepared in a tumbling mixer or the like. The preferred materials are cane sugar, corn syrup (a mixture of dextrose and dextrine in water), dextrose, sodium citrate, and polyethylene glycol.

Concentrations of 0.2% up to 2% or even higher of any one of these materials may be employed, such concentrations being calculated as solids introduced into the fixing powder. The dust bonding material is introduced as a finely atomized spray impinging upon the surface of the fixing powder mixture while it is being mixed within a rotating horizontal drum. Suitable rotary mixing apparatus provided with means for spraying aqueous solutions onto fixing powder mixtures is disclosed in the copending U. S. Wiitala and Kridel patent application Ser. No. 420,298 filed April 1, 1954, now Patent 2,708,597 of May 17, 1955. The concentration of solids in the spraying liquid may be varied over relatively wide limits. With corn syrup we find a 30% solids to be advantageous, whereas using polyethylene glycol preferably of a 2,759,823 Patented Aug. 21, 1956 medium molecular weight known commercially as polyethyleneglycol 400, a concentration as low as 4% gives desirable results.

The following examples further illustrate the present invention:

Example 1 Ammonium alum 10 The first 3 components were mixed and sprayed With a solution of 30% corn syrup at a rate corresponding to 1.9% of the total weight of the dry powder. The sprayed powder upon discharge from the tumbling drum was then mixed with the alum and boric acid to complete the formulation. The concentration of corn syrup in the final mix was 0.5%.

Example 2 The first three components were mixed and sprayed with an 8.5% solution of polyethylene glycol at a rate corresponding to 5.77% of weight of the total dry powder.

,The sprayed powder, upon discharge from the tumbling drum, was mixed with the alum and boric acid to complete the formulation. The concentration of polyethylene glycol in the final mix was 0.5

Example 3 In another instance, the first three components of Example 1 were mixed and sprayed with 16.7% aqueous solution of polyethylene glycol at a rate corresponding to 5.77 of the Wight of the total dry powder. The formulation was completed as before and contained 1.0% of polyethylene glycol.

Example 4 In a third preparation, the first three components of Example 1 were sprayed with a 20% aqueous solution of cane sugar at a rate corresponding to 6.2% of the weight of the total dry powder. When the formulation was completed as above, it contained 1.2% of sugar.

Example 5 In a fourth run, the first three components of Example 1 were sprayed with a 20% solution of cane sugar at a rate corresponding to 9.3% of the weight of the total dry powder. The formula was completed as above and contained 1.86% of sugar.

Example 6 In a fifth case, the first three components were sprayed with a 16.7% aqueous solution of sodium citrate corresponding to 6.4% of the weight of the total dry powder. The formula was completed as in Example 2 and contained 1.07% of sodium citrate.

All of the sprayed fixers above were found to be lower in dust than a check sample prepared from the same chemical materials but sprayed with water alone. The experiments were more resistant than the check sample to the disintegrating action of tumbling in partially filled cans for several hours. They were also tested with micro-biological organisms and practically no growth was observed on either the experiment or the check samples.

We claim:

The method of reducing the dustiness of a photographic fixing powder which comprises mixing parts References Cited in the file of this patent UNITED STATES PATENTS Schmitt Mar. 14, 1939 Bodman Sept. 21, 1943 Kleinicke Feb. 17, 1948 Bodrnan Mar. 29, 1949 

